Heater



FIG. 1 is a top plan view of a heater showing our new design;

FIG. 2 is a bottom plan view thereof;

FIG. 3 is a front elevation view thereof;

FIG. 4 is a back elevation view thereof;

FIG. 5 is a left side elevation view thereof; and,

FIG. 6 is a right side elevation view thereof.

The broken lines in the drawings illustrate subject matter that forms no part of the claimed design. 

CLAIM The ornamental design for a heater, as shown and described. 